U.S. patent number 10,285,280 [Application Number 14/434,024] was granted by the patent office on 2019-05-07 for conductive adhesive for screen printing, joined body of inorganic material, and method for producing same.
This patent grant is currently assigned to Mitsuboshi Belting Ltd.. The grantee listed for this patent is MITSUBOSHI BELTING LTD.. Invention is credited to Taisuke Iseda, Masahiro Iwamoto, Kazutomo Kawahara.
United States Patent |
10,285,280 |
Iseda , et al. |
May 7, 2019 |
Conductive adhesive for screen printing, joined body of inorganic
material, and method for producing same
Abstract
The present invention relates to a conductive adhesive for
screen printing containing metal colloid particles (A) containing
metal nanoparticles (A1) and a protective colloid (A2) containing
an organic compound having a carboxyl group and a polymer
dispersant having a carboxyl group, a viscosity modifier (B) having
an amide bond and/or a urea bond, and a dispersion solvent (C).
Inventors: |
Iseda; Taisuke (Hyogo,
JP), Kawahara; Kazutomo (Hyogo, JP),
Iwamoto; Masahiro (Hyogo, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
MITSUBOSHI BELTING LTD. |
Kobe-shi, Hyogo |
N/A |
JP |
|
|
Assignee: |
Mitsuboshi Belting Ltd. (Hyogo,
JP)
|
Family
ID: |
50626759 |
Appl.
No.: |
14/434,024 |
Filed: |
December 21, 2012 |
PCT
Filed: |
December 21, 2012 |
PCT No.: |
PCT/JP2012/083366 |
371(c)(1),(2),(4) Date: |
April 07, 2015 |
PCT
Pub. No.: |
WO2014/068798 |
PCT
Pub. Date: |
May 08, 2014 |
Prior Publication Data
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|
|
|
Document
Identifier |
Publication Date |
|
US 20150282330 A1 |
Oct 1, 2015 |
|
Foreign Application Priority Data
|
|
|
|
|
Oct 31, 2012 [JP] |
|
|
2012-239957 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09J
11/04 (20130101); C09J 9/02 (20130101); B22F
1/0022 (20130101); C09J 177/00 (20130101); H05K
3/321 (20130101); B22F 1/0074 (20130101); C09J
11/08 (20130101); C09J 177/00 (20130101); C08K
9/08 (20130101); B22F 7/064 (20130101); C08K
2201/011 (20130101); Y10T 156/10 (20150115); Y10T
428/24851 (20150115); H05K 2203/1131 (20130101); B22F
2001/0066 (20130101); C08K 9/08 (20130101) |
Current International
Class: |
H05K
3/32 (20060101); C09J 11/08 (20060101); B22F
1/00 (20060101); C09J 9/02 (20060101); C09J
11/04 (20060101); C09J 177/00 (20060101); C08K
9/08 (20060101); B22F 7/06 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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101206939 |
|
Jun 2008 |
|
CN |
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102300415 |
|
Dec 2011 |
|
CN |
|
102490423 |
|
Jun 2012 |
|
CN |
|
2008-258147 |
|
Oct 2008 |
|
JP |
|
4247801 |
|
Apr 2009 |
|
JP |
|
2010-031182 |
|
Feb 2010 |
|
JP |
|
2010-131669 |
|
Jun 2010 |
|
JP |
|
2010-150653 |
|
Jul 2010 |
|
JP |
|
2010150653 |
|
Jul 2010 |
|
JP |
|
2011-080147 |
|
Apr 2011 |
|
JP |
|
2011-094223 |
|
May 2011 |
|
JP |
|
2011-216475 |
|
Oct 2011 |
|
JP |
|
2012-043545 |
|
Mar 2012 |
|
JP |
|
2011/007402 |
|
Jan 2011 |
|
WO |
|
2012/043545 |
|
Apr 2012 |
|
WO |
|
Other References
"BYK Additive & Instruments Press Release," Jun. 24, 2008.
cited by examiner .
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translation. cited by applicant .
Notification of Reasons for Refusal issued in corresponding
Japanese Application No. 2012-239957, drafted Aug. 3, 2015, dated
Aug. 11, 2015, 9 pages with an English translation. cited by
applicant .
Office Action issued in corresponding Chinese Application No.
201280076609.6, dated Nov. 25, 2016, 14 pages with English
translation. cited by applicant .
Office Action issued in corresponding Taiwanese Application No.
101150653, dated Jan. 22, 2016, 9 pages with English translation.
cited by applicant .
Office Action issued in Japanese Patent Application No. 2012-239957
dated Mar. 10, 2015--12 pages. cited by applicant .
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No. 201280076609.6, dated Jun. 21, 2016, 12 pages with translation.
cited by applicant .
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.
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10-2015-7011203, dated Feb. 6, 2018, 12 pages with an English
translation. cited by applicant .
Office Action issued in corresponding European Patent Application
No. 12887449.2, dated Oct. 19, 2018, 8 pages. cited by applicant
.
Jillavenkatesa, et al., "Particle Size Characterization", NIST
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Retrieved from Internet on Mar. 8, 2019:
https://ws680.nist.gov/publication/get_pdf.cfm?pub_id=850451. cited
by applicant.
|
Primary Examiner: Rummel; Ian A
Attorney, Agent or Firm: Hamre, Schumann, Mueller &
Larson, P.C.
Claims
The invention claimed is:
1. A conductive adhesive for screen printing, comprising: metal
colloid particles (A) containing metal nanoparticles (A1) and a
protective colloid (A2) containing an organic compound having a
carboxyl group and a polymer dispersant having a carboxyl group; a
viscosity modifier (B) having a urea-modified polyamide skeleton;
and a dispersion solvent (C), wherein the dispersion solvent (C)
has a boiling point under atmospheric pressure of 220.degree. C. or
higher and plural hydroxyl groups per molecule, the viscosity
modifier (B) has a polyoxy-C.sub.2-4-alkylene group and/or an alkyl
group, and the viscosity modifier (B) is a compound represented by
the formula (1): R.sup.1-A-U-R.sup.2-U-A-R.sup.1, where R.sup.1 is
a hydroxy (poly)C.sub.2-4-alkoxy group or an alkyl group; A is a
urea-modified polyamide group; U is a urea group; and R.sup.2 is a
(poly)oxy-C.sub.2-4-alkylene group or an alkylene group.
2. The conductive adhesive for screen printing according to claim
1, wherein a proportion of the viscosity modifier (B) is from 1 to
4 parts by mass based on 100 parts by mass of the metal
nanoparticles (A1).
3. The conductive adhesive for screen printing according to claim
1, wherein a proportion of the protective colloid (A2) is from 1 to
3 parts by mass based on 100 parts by mass of the metal
nanoparticles (A1).
4. A production method of a joined body of inorganic materials,
comprising: subjecting the conductive adhesive for screen printing
of claim 1 to screen printing on a joining surface of a first
inorganic material; installing a joining surface of a second
inorganic material on the conductive adhesive printed on the
joining surface of the first inorganic material; and sandwiching
the conductive adhesive by both of the first and the second
inorganic materials, and then heating at 100.degree. C. or higher
to sinter the conductive adhesive to form a sintered film between
the first and the second inorganic materials, wherein the sintered
film has a thickness from 1 to 50 .mu.m.
5. The production method according to claim 4, wherein the joining
surface of at least one of the first and second inorganic materials
contains a noble metal.
6. The conductive adhesive for screen printing according to claim
1, wherein the urea-modified polyamide skeleton accounts for 10 to
80% by mass of the viscosity modifier (B).
7. The conductive adhesive for screen printing according to claim
1, wherein a number-average molecular weight of the viscosity
modifier (B) is from 50,000 to 150,000.
Description
TECHNICAL FIELD
The present invention relates to a conductive adhesive for screen
printing which can be utilized for formation of electrodes or
circuits of electronic components and the like, adhesion between
components and the like, and to a joined body of inorganic material
using this adhesive and a method for producing the same.
BACKGROUND ART
At the present time, conductive pastes such as silver pastes are
used for forming electrodes or circuits of electronic components
and the like. In addition, the conductive pastes are also used as a
conductive adhesive and used for adhesion between the components
and the like. As for the characteristics required as the conductive
adhesive, there are mentioned, in addition to conductivity, thermal
conductivity for releasing heat generated in an electronic
component to the outside. In general, specific resistivity and
coefficient of thermal conductivity of metal have correlation to
each other, and according to the Wiedemann-Franz law, it is
expressed by .lamda.=L.times.T/.rho.v (in the formula, .lamda. is a
coefficient of thermal conductivity of metal; L is the Lorenz
number; T is an absolute temperature; and .rho.v is a specific
resistivity). That is, this law indicates that the lower the
specific resistivity of conductive film, the higher the coefficient
of thermal conductivity is. For that reason, metals having a low
specific resistivity, such as silver, are also excellent from the
standpoint of thermal conductivity.
Patent Document 1 discloses a conductive paste containing silver
nanoparticles having a particle diameter of 100 nm or less, a
protective colloid constituted of an organic compound having a
carboxyl group and a polymer dispersant, and a solvent. When this
conductive paste is baked at 100.degree. C. or higher to remove the
solvent, the silver nanoparticles are sintered, whereby a
conductive film composed of a metallic bond is formed, and
therefore, it is possible to form a conductive metal film close to
a bulk. In addition, this patent document describes that in the
case where an adherend surface is a noble metal, the silver
nanoparticles are sintered on the adherend surface to undergo
metallic bonding, and therefore, joining composed of a metallic
bond is achieved, and it becomes possible to achieve joining with
tremendously low resistivity and high heat radiation properties.
Furthermore, in this patent document, after the above-described
conductive paste is coated on a one-sided adherend (a so-called
substrate or lead frame), the other-sided adherend (a so-called
chip) is installed on the coated conductive paste, and the coated
conductive paste is sandwiched by the both adherends, followed by
heating to achieve adhesion.
However, according to a method of using this conductive paste
(adhesive), productivity is low and a use application thereof is
also limited. That is, in the above-described method, when the
solvent of the coated adhesive is volatilized and dried prior to
installation of a chip on the coated conductive paste, even if the
chip is installed, the conductive paste does not adhere to the
chip. Drying of the adhesive becomes faster when a coating area is
smaller and furthermore, when a coating thickness is thinner. In a
chip packaging step, there is frequently found the case where after
coating the adhesive and then elapsing several hours, chip mounting
is performed. In order to respond to such a step, a method of
delaying a volatilization rate of the solvent to be used for the
adhesive is necessary. In particular, in joining an LED
(light-emitting diode) chip, since a joining area is several
hundred .mu.m.quadrature. (several hundred .mu.m.times.several
hundred .mu.m) or less, drying of the adhesive is particularly
fast. In coating of an adhesive by means of dispensing or pin
transfer, since the coated adhesive is coated or transferred in a
thickness of 100 .mu.m or more, though drying of the adhesive is
slow, a coating thickness of the adhesive varies and extrusion of
the adhesive or the like is caused. Therefore, coating of the
adhesive by means of dispensing or pin transfer is unsuitable in
LED packaging in which high positioning precision is required. In
addition, because a superfluous excess of the adhesive is coated,
the costs become high.
As a high-precision and inexpensive coating method, there is
mentioned a screen printing. According to the screen printing, an
adhesive can be coated in a thickness of about several ten .mu.m,
and as compared with dispensing or pin transfer, it is possible to
coat a printing pattern with high precision. In the screen
printing, viscosity and rheology of a paste are important. In order
to control the viscosity and rheology of a paste, in general
conductive adhesives, resins having both adhesiveness and viscosity
are used. However, in the case of using a general conductive
adhesive, an interface between metal nanoparticles and an adherend
surface or a gap between metal nanoparticles, is continuity due to
physical contact, and hence, the electrical resistance value and
heat radiation properties are lowered. Meanwhile, the metal
nanoparticles has a surface protective agent composed of a
surfactant chemically adsorbed on the surface thereof, and
therefore, by choosing the surface protective agent, printing
properties can be ensured. It is to be noted that in a metal
nanoparticle paste having excellent printing properties, in
general, a large quantity of the surface protective agent is
adsorbed on the metal nanoparticles. In this case, since sintering
between the metal nanoparticles is hindered, joining is difficult.
So far as a paste in which the quantity of the surface protective
agent is small relative to the metal nanoparticles is concerned,
though it is possible to achieve rheology suitable for screen
printing by increasing the metal concentration, in this case,
drying after coating the adhesive becomes extremely fast.
It is to be noted that Patent Document 2 discloses, as a resin
composition for forming an insulating protective film, a resin
composition containing a resin having at least one bond derived
from an acid anhydride group and/or a carboxyl group, inorganic
fine particles, and a urea-modified polyamide compound and/or a
urea urethane. This patent document describes that the printing
precision of screen printing or the like is improved. This patent
document describes that the urea-modified polyamide compound and/or
urea urethane is used as a viscosity modifier. In the working
examples thereof, a resin composition containing a resin having a
carbonate skeleton, inorganic particles such as silica particles or
barium sulfate particles, and the above-describe viscosity modifier
was subjected to screen printing and then heated for curing,
thereby forming a resin coating film.
However, this patent document does not describe an interaction
between the inorganic fine particles and the viscosity
modifier.
PRIOR ART DOCUMENT
Patent Document
Patent Document 1: JP-A-2010-150653
Patent Document 2: JP-A-2010-31182
SUMMARY OF THE INVENTION
Problem to be Solved by the Invention
In consequence, an object of the present invention is to provide a
conductive adhesive in which after performing screen printing, high
conductivity and adhesiveness to an inorganic material can be
imparted by heating, and a joined body using this adhesive and also
a method for producing the same.
Another object of the present invention is to provide a conductive
adhesive in which even when a fine pattern is formed by means of
screen printing, productivity is high and heat radiation properties
and adhesiveness to an inorganic material can be improved, and a
joined body of inorganic materials using this adhesive and also a
method for producing the same.
Means for Solving the Problem
In order to solve the above-described problem, the present
inventors made extensive and intensive investigations. As a result,
it has been found that by combining metal colloid particles (A)
containing metal nanoparticles (A1) and a protective colloid (A2)
containing an organic compound having a carboxyl group and a
polymer dispersant having a carboxyl group, a viscosity modifier
(B) having an amide bond and/or a urea bond, and a dispersion
solvent (C), after performing screen printing, high conductivity
and adhesiveness to an inorganic material can be imparted by
heating, leading to accomplishment of the present invention.
That is, the conductive adhesive for screen printing according to
the present invention contains:
metal colloid particles (A) containing metal nanoparticles (A1) and
a protective colloid (A2) containing an organic compound having a
carboxyl group and a polymer dispersant having a carboxyl
group;
a viscosity modifier (B) having an amide bond and/or a urea bond;
and
a dispersion solvent (C).
The viscosity modifier (B) may have a urea-modified polyamide
skeleton.
The viscosity modifier (B) may further have a
polyoxy-C.sub.2-4-alkylene group and/or an alkyl group.
The proportion of the viscosity modifier (B) is preferably from 1
to 4 parts by mass based on 100 parts by mass of the metal
nanoparticles (A1).
The proportion of the protective colloid (A2) is preferably from 1
to 3 parts by mass based on 100 parts by mass of the metal
nanoparticles (A1).
The dispersion solvent (C) may be a solvent having a boiling point
under atmospheric pressure of 220.degree. C. or higher and having
plural hydroxyl groups in a molecule thereof.
Further, the present invention provides a production method of a
joined body of inorganic materials, containing:
a printing step of subjecting the conductive adhesive for screen
printing to screen printing on a joining surface of a first
inorganic material; and
a sintering step of installing a joining surface of a second
inorganic material on the printed conductive adhesive, sandwiching
the conductive adhesive by the both inorganic materials, and then
heating at 100.degree. C. or higher to sinter the conductive
adhesive.
In this production method, the joining surface of at least one of
the first and second inorganic materials may contain a noble
metal.
Furthermore, the present invention provides a joined body of
inorganic materials obtained by the production method.
Effects of the Invention
In the present invention, by combining metal colloid particles (A)
containing metal nanoparticles (A1) and a protective colloid (A2)
containing an organic compound having a carboxyl group and a
polymer dispersant having a carboxyl group, a viscosity modifier
(B) having an amide bond and/or a urea bond, and a dispersion
solvent (C), even when a use amount of the viscosity modifier (B)
is small, thickening is possible; and since the viscosity modifier
(B) having an amide bond and/or a urea bond is hardly accumulated
at a base material surface/metal nanoparticle interface (adherend
surface), the metal nanoparticles (A1) are easy to come into
contact with an inorganic material, and after performing screen
printing, high conductivity and adhesiveness to the organic
material can be imparted by heating. That is, in the present
invention, even when the adhesive is thickened to an extent
necessary for screen printing properties, high conductivity can be
imparted to a baked film, and it is possible to make both screen
printing properties and conductivity, which have hitherto been
characteristics conflicting with each other, compatible with each
other. Furthermore, even when a fine pattern is formed by means of
screen printing, productivity is high, and heat radiation
properties and adhesiveness to an inorganic material can also be
improved.
MODES FOR CARRYING OUT THE INVENTION
[Conductive Adhesive for Screen Printing]
The conductive adhesive for screen printing according to the
present invention contains metal colloid particles (A) containing
metal nanoparticles (A1) and a protective colloid (A2) containing
an organic compound having a carboxyl group and a polymer
dispersant having a carboxyl group, a viscosity modifier (B) having
an amide bond and/or a urea bond, and a dispersion solvent (C).
As for the conductive adhesive, it is an ideal to ensure
conductivity (and heat radiation properties) and adhesiveness to a
base material (inorganic material) through bonding between the
metal nanoparticles (A1) and also between the metal nanoparticles
(A1) and the base material. However, in conventional conductive
adhesives, in the case of a conductive adhesive composed of a
mixture of metal particles and a binder resin (e.g., an epoxy
resin), though adhesiveness to the base material is revealed due to
the binder resin, only a physical contact is generated but metallic
bonding is not caused, and therefore, sufficient conductivity is
not obtained. In the case of a conductive adhesive composed of only
metal nanoparticles and a solvent without using a binder resin
(e.g., the conductive adhesives described in Patent Document 1),
conductivity and adhesiveness can be ensured through metallic
bonding. However, screen printing properties (e.g., appropriate
viscosity and rheology) are insufficient and therefore are adjusted
by adding, as a thickening agent, a polymer component (e.g., ethyl
cellulose). However, the thickening agent is easily accumulated at
a base material surface/metal nanoparticle interface (adherend
surface), and adhesion by metallic bonding is hindered.
In the present invention, by using the above-described viscosity
modifier (B) as the polymer component which is not accumulated at a
base material surface/metal nanoparticle interface (adherend
surface), the polymer component is not accumulated at the base
material surface/metal nanoparticle interface (adherend surface),
and hence, a bond between the base material and the metal
nanoparticles (A1) is easily generated, and adhesiveness and
conductivity through metallic bonding can be ensured. Further, the
viscosity modifier (B) has a thickening effect by its addition in a
small amount. For that reason, when the viscosity modifier (B) is
used, even if a resin for an adhesion purpose (binder resin) is
absent, adhesiveness can be ensured, and conductivity can be
ensured while ensuring screen printing properties (e.g.,
appropriate viscosity and rheology).
It may be assumed that such effects of the present invention are
revealed through hydrogen bonding between a hydrogen bond-forming
group (e.g., an amide group and/or a urea group, etc.) which the
viscosity modifier (B) has and a carboxyl group of the protective
colloid (A2) surrounding the metal nanoparticles (A1). That is, it
may be assumed that the viscosity modifier (B) is made adhere to
the protective colloid (A2) through hydrogen bonding to become
hardly accumulated at a base material surface/metal nanoparticle
interface (adherend surface) (i.e., a speed at which the metal
nanoparticles (A1) bond to the base material is faster than a speed
at which the viscosity modifier (B) is accumulated at the base
material surface/metal nanoparticle interface (adherend surface));
and that not only the metallic bond formation between the metal
nanoparticles (A1) and the base material is promoted, but also the
hydrogen bond-forming group which the viscosity modifier (B)
undergoes hydrogen bonding to the solvent molecule or the
protective colloid (A2), whereby the thickening effect is also
revealed, and the screen printing becomes easy.
(A) Metal colloid particles:
The metal colloid particles (A) only have to contain the metal
nanoparticles (A1) and the protective colloid (A2) containing an
organic compound having a carboxyl group and a polymer dispersant
having a carboxyl group. Although the metal nanoparticles (A1) and
the protective colloid (A2) may be present independently of each
other, from the standpoint that dispersibility of the metal
nanoparticles (A1) can be improved, the metal colloid particles (A)
constituted of the metal nanoparticles (A1) and the protective
colloid (A2) covering those metal nanoparticles (A1) may also be
adopted.
(A1) Metal nanoparticles:
Examples of a metal (metal atom) that constitutes the metal
nanoparticles (A1) include transition metals (e.g., metals
belonging to Group 4A of the periodic table, such as titanium,
zirconium, etc.; metals belonging to Group 5A of the periodic
table, such as vanadium, niobium, etc.; metals belonging to Group
6A of the periodic table, such as molybdenum, tungsten, etc.;
metals belonging to Group 7A of the periodic table, such as
manganese, etc.; metals belonging to Group 8 of the periodic table,
such as iron, nickel, cobalt, ruthenium, rhodium, palladium,
rhenium, iridium, platinum, etc.; metals belonging to Group 1B of
the periodic table, such as copper, silver, gold, etc.; etc.),
metals belonging to Group 2B of the periodic table (e.g., zinc,
cadmium, etc.), metals belonging to Group 3B of the periodic table
(e.g., aluminum, gallium, indium, etc.), metals belonging to Group
4B of the periodic table (e.g., germanium, tin, lead, etc.), metals
belonging to Group 5B of the periodic table (for example, antimony,
bismuth, etc.), and the like. The metal may also be a metal
belonging to Group 8 of the periodic table (e.g., iron, nickel,
rhodium, palladium, platinum, etc.), a metal belonging to Group 1B
of the periodic table (e.g., copper, silver, gold, etc.), a metal
belonging to Group 3B of the periodic table (e.g., aluminum, etc.),
a metal belonging to Group 4B of the periodic table (e.g., tin,
etc.), or the like. It is to be noted that in many cases, the metal
(metal atom) is a metal having high coordination properties to the
protective colloid (A2), for example, a metal belonging to Group 8
of the periodic table, a metal belonging to Group 1B of the
periodic table, or the like.
The metal nanoparticles (A1) may also be a simple substance of the
above-described metal, an alloy of the above-described metal, a
metal oxide, a metal hydroxide, a metal sulfide, a metal carbide, a
metal nitride, a metal boride, or the like. Those metal
nanoparticles (A1) can be used solely or in combination of two or
more kinds thereof. In many cases, the metal nanoparticles (A1) are
generally a metal simple substance particle or a metal alloy
particle. Above all, the metal constituting the metal nanoparticles
(A1) is preferably a metal (a metal simple substance and a metal
alloy) containing at least a noble metal (especially a metal
belonging to Group 1B of the periodic table), such as silver, etc.,
and especially a noble metal simple substance (e.g., a silver
simple substance, etc.).
The metal nanoparticles (A1) are in a nanometer size. A volume
basis center particle diameter (primary particle diameter) of the
metal nanoparticles (A1) can be chosen within the range of from
about 1 to 150 nm, and it is, for example, from about 10 to 150 nm,
preferably from about 15 to 120 nm, and more preferably from about
20 to 100 nm. When the particle diameter is too small, a specific
area of the nanoparticle is large, so that a proportion of the
protective colloid (A2) covering the surface becomes large, the
protective colloid (A2) is hardly removed even by baking, and a
metallic bonding is easily hindered. Meanwhile, when the particle
diameter is too large, sintering hardly occurs, and the formation
of a metallic bond becomes difficult.
(A2) Protective colloid:
The protective colloid (A2) contains an organic compound having a
carboxyl group (carboxy organic compound) and further contains a
polymer dispersant having a carboxyl group.
The carboxy organic compound has a carboxyl group. The number of
such carboxyl groups is not particularly limited so long as it is
one or more per a molecule of the carboxy organic compound, and it
may be preferably from about 1 to 3. It is to be noted that in the
carboxy organic compound, a part or all of the carboxyl groups may
form a salt (e.g., a salt with an amine, a metal salt, etc.). In
particular, in the present invention, an organic compound in which
the carboxyl group (especially all carboxyl groups) does not form a
salt [especially a salt with a basic compound (e.g., a salt with an
amine, an amine salt, etc.)] (i.e., an organic compound having a
free carboxyl group) can be suitably used.
As the carboxy organic compound, the compounds having a carboxyl
group as described in the above-mentioned Patent Document 1 can be
used solely or in combination with two or more kinds thereof. Among
the compounds having a carboxyl group as described in the
above-mentioned Patent Document 1, a saturated aliphatic carboxylic
acid having a free carboxyl group and having a relatively low
molecular weight is preferable from the standpoint that it
separates from the metal particles or disappears at a baking
temperature and forms a sintering site to improve a joining force
of the inorganic material. Examples thereof include a
C.sub.1-16-alkanoic acid (alkanecarboxylic acid), such as formic
acid, acetic acid, propionic acid, butyric acid, valeric acid,
etc., preferably a C.sub.1-12-alkanoic acid (e.g., a
C.sub.1-6-alkanoic acid), more preferably a C.sub.1-4-alkanoic
acid, and especially a C.sub.1-3-alkanoic acid (e.g., a
C.sub.1-2-alkanoic acid such as acetic acid, etc.).
It is to be noted that a molecular weight of the carboxy organic
compound may be, for example, 1,000 or less (e.g., from about 46 to
900), preferably 600 or less (e.g., from about 46 to 500), and more
preferably 100 or less (e.g., from about 46 to 74).
In addition, a pKa value of the carboxy organic compound may be,
for example, 1 or more (e.g., from about 1 to 10), and preferably 2
or more (e.g., from about 2 to 8).
By combining the above-described carboxy organic compound with a
polymer dispersant having a carboxyl group, nevertheless an amount
of coarse particles is small, a proportion of the metal
nanoparticles (A1) can be made large and storage stability of the
metal colloid particles (A) (and a dispersion liquid thereof) in
the paste can also be improved.
As the polymer dispersant having a carboxyl group, the polymer
dispersants described in the above-mentioned Patent Document 1 can
be used solely or in combination with two or more kinds thereof
Among the polymer dispersants described in Patent Document 1,
poly(meth)acrylic acids [or polyacrylic acid-based resins, for
example, poly(meth)acrylic acid, a polymer composed of
(meth)acrylic acid as a main component, such as a copolymer of
(meth)acrylic acid and a copolymerizable monomer (e.g., a
(meth)acrylate, maleic anhydride, etc.), etc., and a salt thereof
(e.g., an alkali metal salt such as sodium polyacrylate, etc.,
etc.), or the like], DISPERBYK 190 (manufactured by BYK-Chemie
Japan K.K.), DISPERBYK 194 (manufactured by BYK-Chemie Japan K.K.),
and the like can be preferably utilized.
A number-average molecular weight of the polymer dispersant having
a carboxyl group can be chosen within the range of from 1,000 to
1,000,000, and it is, for example, from about 1,500 to 500,000,
preferably from about 2,000 to 80,000, and more preferably from
about 3,000 to 50,000 (especially from 5,000 to 30,000).
A proportion of the carboxy organic compound and the polymer
dispersant having a carboxyl group (a proportion of solids in the
case of containing a solvent and the like) may be as follow: the
former/the latter (mass ratio)=from about 99.9/0.1 to 1/99,
preferably from about 99/1 to 5/95, and more preferably from about
95/5 to 10/90 (especially from 95/5 to 50/50).
A proportion of the protective colloid (A2) is, for example, from
about 0.1 to 10 parts by mass, preferably from about 0.3 to 8 parts
by mass, and more preferably from about 0.5 to 5 parts by mass
(especially from 1 to 3 parts by mass), as converted into solid
contents, based on 100 parts by mass of the metal nanoparticles
(A1). When the proportion of the protective colloid (A2) is too
small, a proportion of coarse metal nanoparticles becomes large,
whereas when it is too large, there may be the case where the
metallic bonding is hindered and the conductivity is lowered.
(B) Viscosity modifier:
The viscosity modifier (i.e., a thickener or a rheology-controlling
agent) (B) is an additive capable of undergoing hydrogen bonding to
the carboxyl group contained in the protective colloid (A2) in the
adhesive. In order to make it possible to undergo hydrogen bonding
to the carboxyl group, it has a hydrogen atom and an
electronegative atom (e.g., an oxygen atom and/or a nitrogen atom)
in a molecule thereof, and from the standpoints that bonding
strength of the hydrogen bond is large and that thickening
properties and compatibility with the solvent are high, it has an
amide bond and/or a urea bond (especially an amide bond). For that
reason, the amide bond and/or the urea bond undergoes an
interaction with the protective colloid (A2), and as a result, even
if its addition amount is small, it is possible to significantly
improve the viscosity of the pasty adhesive, and screen printing
properties can be improved. In addition, in the case of the
viscosity modifier (B) that reveals such hydrogen bonding, at the
time of curing of the adhesive, the viscosity modifier (B) is
hardly accumulated on the adherend surface of the base material and
hardly hinders metallic joining.
On the other hand, in the case of a polymer (resin) that does not
undergo hydrogen bonding to the protective colloid (A2) or a
polymer having small bonding strength of the hydrogen bond to the
protective colloid (A2), under curing conditions, the resin is
easily accumulated at the base material surface/metal nanoparticle
interface before a sintering reaction (metallic bonding) of the
metal nanoparticles (A1) on the noble metal surface of the base
material is generated, and metallic bonding is hardly generated
(i.e., a speed at which the resin is accumulated at the base
material surface/metal nanoparticle interface is faster than a
sintering speed of the metal nanoparticles on the base material
surface). Meanwhile, in the case of the viscosity modifier (B)
capable of undergoing hydrogen bonding to the protective colloid
(A2) (a viscosity modifier acting as a hydrogen bonding assistant),
a part or the whole of the viscosity modifier (B) is restrained by
the hydrogen bonding to the protective colloid (A2), and therefore,
it may be assumed that under curing conditions, the sintering
reaction (metallic bonding) of the metal nanoparticles (A1) is
generated faster than the accumulation of the viscosity modifier
(B) on the surface of the base material, whereby metallic joining
can be achieved (i.e., a sintering speed of the metal nanoparticles
(A1) on the base material surface is faster than a speed at which
the viscosity modifier (B) is accumulated at the base material
surface/metal nanoparticle interface).
As for the viscosity modifier (B), a structure in which hydrogen
bonding to the carboxyl group of the protective colloid (A2) is
easily undergone is preferable, and a structure having a
urea-modified polyamide skeleton is especially preferable.
In order to improve dispersibility in the adhesive, the viscosity
modifier (B) may have, in addition to the above-described polyamide
skeleton (especially a urea-modified polyamide skeleton), a
(poly)oxy-C.sub.2-4-alkylene group (e.g., a hydroxyethoxy group, a
polyoxyethylene group, a hydroxypropoxy group, a polyoxypropylene
group, etc.) or an alkyl group (e.g., a C.sub.1-12-alkyl group such
as a methyl group, an ethyl group, a butyl group, etc.). These
groups may be included solely or in combination with two or more
kinds thereof (e.g., a combination of a (poly)oxyethylene group, a
(poly)oxypropylene group, and an alkyl group, etc.). Of these, a
(poly)oxy-C.sub.2-4-alkylene group (especially a (poly)oxyethylene
group) is excellent in dispersibility in a hydrophilic dispersion
solvent, and an alkyl group is excellent in dispersibility in a
hydrophobic dispersion solvent.
The viscosity modifier (B) may also be a compound represented by
the formula (1): R.sup.1-A-U-R.sup.2-U-A-R.sup.1 (in the formula,
R.sup.1 is a hydroxy (poly)C.sub.2-4-alkoxy group or an alkyl
group; A is a urea-modified polyamide group; U is a urea group; and
R.sup.2 is a (poly)oxy-C.sub.2-4-alkylene group or an alkylene
group).
In the viscosity modifier (B) having a polyamide skeleton
(especially a urea-modified polyamide skeleton), a proportion of
the polyamide skeleton (especially a urea-modified polyamide
skeleton) is, for example, from about 1 to 95% by mass, preferably
from about 5 to 90% by mass, and more preferably from about 10 to
80% by mass relative to the whole of the viscosity modifier
(B).
A number-average molecular weight of the viscosity modifier (B) is,
for example, from about 1,000 to 1,000,000, preferably from about
5,000 to 500,000, and more preferably from about 10,000 to 200,000
(especially from 50,000 to 150,000).
A proportion of the viscosity modifier (B) is, for example, from
about 0.1 to 10 parts by mass, preferably from about 0.3 to 8 parts
by mass, and more preferably from about 0.5 to 5 parts by mass
(especially from 1 to 4 parts by mass), as converted into solid
contents, based on 100 parts by mass of the metal nanoparticles
(A1). When the proportion of the viscosity modifier (B) is too
small, an action of the hydrogen bonding to the protective colloid
(A2) of the metal nanoparticles (A1) is small and liquid dripping
easily occurs, and therefore, there may be the case where screen
printing becomes difficult. Meanwhile, when the proportion of the
viscosity modifier (B) is too large, there may be the case where
metallic joining with the adherend surface becomes difficult.
(C) Dispersion solvent:
Although the dispersion solvent (C) only has to be able to disperse
the above-described metal nanoparticles (A1) (or the metal colloid
(A)) in the adhesive, a solvent whose boiling point under
atmospheric pressure is 220.degree. C. or higher is preferable from
the standpoint of screen printing properties. The boiling point
under atmospheric pressure of the dispersion solvent (C) is, for
example, from about 220 to 300.degree. C., preferably from about
230 to 280.degree. C., and more preferably from about 240 to
270.degree. C. When the boiling point of the dispersion solvent (C)
is too low, in the case of coating the conductive adhesive by means
of screen printing to form a pattern having, for example, a
thickness of from about 5 to 20 .mu.m and a width of from about 30
to 100 .mu.m, drying is so vigorous that the solvent is dried
before performing chip package mounting, whereby adhesion failure
is easily caused. Meanwhile, when the boiling point is too high,
the solvent is hardly volatilized under curing conditions of the
conductive adhesive (generally at from 100 to 300.degree. C. for
from 3 to 120 minutes), the adhesive layer is easily damaged, it is
necessary to increase the curing temperature or to prolong the
curing time, and deterioration of a semiconductor chip or reduction
of productivity is easily caused.
Furthermore, as the dispersion solvent (C), a solvent having a
hydroxyl group is preferable from the standpoint that a delay of
drying is easily revealed. In particular, when a solvent having
plural hydroxyl groups (e.g., from 2 to 3 hydroxyl groups, and
preferably two hydroxyl groups) in one molecule is used, it becomes
possible to conduct chip mounting without being dried for several
hours after printing. While a reason why a solvent having two
hydroxyl groups in one molecule (i.e., a diol) is suitable
especially for delaying the drying as compared with an alcohol in
which a boiling point of the solvent is the same degree (i.e., a
solvent having one hydroxyl group in one molecule) is not
elucidated yet, it can be assumed that the hydroxyl groups of the
diol are easily undergo hydrogen bonding to the protective colloid
(A2).
Examples of such a dispersion solvent (C) include an aliphatic
alcohol [e.g., a C.sub.10-20-alcohol such as 1-decanol (229.degree.
C.), 1-undecanol (243.5.degree. C.), 1-tetradecanol (295.degree.
C.), etc.], a cellosolve [e.g., ethylene glycol monophenyl ether
(244.7.degree. C.), diethylene glycol monobutyl ether
(230.4.degree. C.), triethylene glycol monomethyl ether
(249.degree. C.), etc.], an aliphatic diol [e.g., 1,4-butanediol
(229.degree. C.), 1,5-pentanediol (239 to 242.degree. C.), etc.], a
glycol [e.g., diethylene glycol (245.degree. C.)], and an aromatic
diol [e.g., m-xylene-4,6-diol (276 to 279.degree. C.),
p-xylene-2,6-diol (277 to 280.degree. C.), 3,4-toluenediol
(251.degree. C.), 3,4-xylenol (225.degree. C.), etc.]. These
dispersion solvents (C) can be used solely or in combination of two
or more kinds thereof.
Of these dispersion solvents (C), an aliphatic diol, a glycol, and
an aromatic diol are preferable, and an aliphatic diol such as
1,5-pentanediol is especially preferable.
A concentration of the metal nanoparticles (A1) in the conductive
adhesive for screen printing may be, for example, from about 30 to
95% by mass, preferably from about 50 to 93% by mass, and more
preferably from about 60 to 90% by mass (especially from 65 to 85%
by mass). It is to be noted that in the conductive adhesive, the
metal nanoparticles (A1) covered by the protective colloid (A2) are
also in a nanometer size, and a volume basis center particle
diameter (primary particle diameter) thereof and the like can be
chosen within the same range as that described above.
The conductive adhesive for screen printing of the present
invention may contain customary additives, for example, a coloring
agent (e.g., a dye, a pigment, etc.), a hue modifier, a dye fixing
agent, a gloss imparting agent, a metal corrosion preventive, a
stabilizer (e.g., an antioxidant, a UV absorber, etc.), a
surfactant or dispersant (e.g., an anionic surfactant, a cationic
surfactant, a nonionic surfactant, an ampholytic surfactant, etc.),
a dispersion stabilizer, a thickening agent or viscosity modifier
other than the above-described viscosity modifier (B), a humectant,
a thixotropy-imparting agent, a levelling agent, a defoaming agent,
a bactericide, a filler, etc. according to a use application
thereof In addition, it may further contain a binder resin within
the range where the effects of the present invention are not
impaired. These additives can be used solely or in combination of
two or more kinds thereof.
In the conductive adhesive for screen printing of the present
invention, the metal colloid particles (A) can be prepared by a
customary method, for example, a method of reducing a metal
compound corresponding to the above-described metal nanoparticles
(A1) in a solvent in the presence of the protective colloid (A2)
and a reducing agent. In detail, it can be produced by the
production method described in the above-mentioned Patent Document
1, or the like. Furthermore, the conductive adhesive can be
prepared by kneading the metal colloid particles (A) with the
viscosity modifier (B) and the dispersion solvent (C) by using a
mortar or the like. The viscosity modifier (B) and/or the
dispersion solvent (C) may be added dividedly, and the water or
solvent incorporated into the adhesive may be removed by using a
heater such as a dryer, etc.
[Joined Body of Inorganic Materials and Joining Method]
The conductive adhesive for screen printing of the present
invention is suitably used for joining inorganic materials. In
detail, a joined body of inorganic materials is obtained through a
printing step of subjecting the above-described conductive adhesive
to screen printing on a joining surface of a first inorganic
material; and a sintering step of installing a joining surface of a
second inorganic material on the printed conductive adhesive,
sandwiching the conductive adhesive by the both inorganic
materials, and then heating at 100.degree. C. or higher to sinter
the a conductive adhesive. That is, the joined body of inorganic
materials of the present invention is obtained by allowing the
above-described conductive adhesive to intervene between the first
inorganic material and the second inorganic material and sintering
the conductive adhesive.
Although the inorganic material may be an inorganic material such
as glass, a carbon material, etc., since the conductive adhesive
contains the metal nanoparticles (A1), from the standpoint of
increasing a joining force, a material in which at least a joining
surface thereof contains a metal (or a metal is present on a
joining surface) (especially a material in which almost all surface
of a joining surface thereof is constituted of a metal) is
preferable. Examples of the metal include the metal simple
substance, alloy and metal compound exemplified in the section of
the metal nanoparticles (A1), and the like. Of these, a metal
simple substance or alloy is preferable. A combination of a metal
simple substance that constitutes the metal nanoparticles (A1) and
a metal simple substance that constitutes the joining surface of
the inorganic material (or each of metal simple substances that
constitute an ally) may be selected according to a crystal
structure such as a simple cubic lattice structure (sc), a
face-centered cubic lattice structure (fcc), a body-centered cubic
lattice structure (bcc), a hexagonal close-packed structure (hcp),
etc. It may be a combination of different crystal structures, but a
combination of the same crystal structures (e.g., a combination of
fcc structures, a combination of bcc structures, etc.) is
preferable. In addition, it is preferable that lattice constants
are close to each other, too, and a lattice constant of the metal
simple substance that constitutes the joining surface may be from
about 0.8 to 1.2 times (especially from 0.86 to 1.17 times)
relative to a lattice constant of the metal simple substance that
constitutes the metal nanoparticles (A1). It may be assumed that
when the lattice constants of the both are adjusted so as to fall
within such a range, the mutual crystal lattices are coordinated
with each other, so that a good metallic bond is formed at the
interface. In addition, an atomic radius of the metal simple
substance that constitutes the joining surface may be from about
0.8 to 1.2 times (especially from 0.85 to 1.15 times) relative to
an atomic radius of the metal simple substance that constitutes the
metal nanoparticles (A1). When the atomic radiuses of the both are
adjusted so as to fall within such a range, solubilities of the
mutual atoms are large, so that they are easily melted together at
the interface. For example, in the case where the metal
nanoparticles (A1) are constituted of silver (fcc, lattice constant
a: 3.614 .ANG. (angstroms), atomic radius: 1.422 .ANG.), the metal
that constitutes the joining surface is preferably at least a metal
(e.g., a metal simple substance and a metal alloy) containing a
noble metal (especially a metal belonging to Group 1B of the
periodic table) such as silver, gold (fcc, lattice constant a:
4.078 .ANG., atomic radius: 1.439 .ANG.), etc., copper (fcc,
lattice constant a: 3.614 .ANG., atomic radius: 1.276 .ANG.),
nickel (fcc, lattice constant a: 3.524 .ANG., atomic radius: 1.244
.ANG.), or the like, and especially a noble metal simple substance
(e.g., a gold or palladium (fcc, lattice constant a: 3.89 .ANG.,
atomic radius: 1.373 .ANG.) simple substance, etc.). That is, in
the case where the base material is constituted of a metal compound
such as aluminum nitride (AlN), aluminum oxide (Al.sub.2O.sub.3),
etc., or a nonmetal, it is preferable to subject the joining
surface to a surface treatment with a metal simple substance or a
metal alloy. Examples of the surface treatment method include
sputtering or plating with a metal containing a noble metal, and
the like. In the case where the joining surface of the inorganic
material contains a metal, though the metal that constitutes the
metal nanoparticles (A1) and the metal contained on the joining
surface of the inorganic material may be different from each other,
they are preferably the same metal or metals belonging to the same
group.
The first inorganic material and the second inorganic material to
be joined may be a different material from each other, or may be
the same material. Although a shape of the inorganic material is
not particularly limited, for example, it may be a shape in which a
contact area between the materials to be joined becomes large, for
example, a shape in which the joining surface is planar (generally
a plate- or sheet-like shape, a film-like shape, or a foil-like
shape), or the like, or may be a wire-like shape or a linear
shape.
As a method of screen printing, a customary method can be utilized.
A coating thickness is from about 1 to 50 .mu.m, preferably from
about 30 to 30 and more preferably from 5 to 20 .mu.m. Furthermore,
in the present invention, it is possible to perform printing with a
fine pattern, and for example, a width (wire diameter) of the
pattern is, for example, from about 10 to 500 .mu.m, preferably
from 20 to 300 .mu.m, and more preferably from about 30 to 100
.mu.m. A screen plate is, for example, from about 100 to 1,000
meshes, preferably from about 200 to 800 meshes, and more
preferably from about 300 to 600 meshes.
A baking temperature for sintering the conductive adhesive only has
to be 100.degree. C. or higher, and it is, for example, from about
100 to 500.degree. C., preferably from about 120 to 400.degree. C.,
and more preferably from about 150 to 350.degree. C. (especially
from 180 to 300.degree. C.). In addition, prior to baking,
preheating may be performed at a temperature of, for example, from
about 80 to 200.degree. C. (especially from 100 to 150.degree. C.).
At the time of baking, a pressure may be applied, and the baking
may be performed in a state of applying a load of, for example,
from about 1 to 500 g/cm.sup.2, preferably from about 3 to 300
g/cm.sup.2, and more preferably from about 5 to 100 g/cm.sup.2. It
is to be noted that the baking may be performed in air, or may be
performed in an inert gas such as a nitrogen gas, an argon gas,
etc.
A baking treatment time (heating time) may be, for example, from
about 1 minute to 10 hours, preferably from about 20 minutes to 5
hours, and more preferably from about 30 minutes to 3 hours
according to the baking temperature and the like.
EXAMPLES
The present invention is hereunder described in more detail on the
basis of the following Examples, but it should not be construed
that the present invention is limited to these Examples. In the
following Examples, measurement methods or evaluation methods in
respective physical properties and raw materials used in the
Examples are shown below. It is to be noted that all "parts" and
"%" are on a mass basis unless otherwise indicated.
Example 1
(Preparation of Silver Colloid Particles)
Into 100 g of ion-exchanged water were charged 66.8 g of silver
nitrate, 10 g of acetic acid (manufactured by Wako Pure Chemical
Industries, Ltd., boiling point: 118.degree. C.) and 0.7 g of a
polymer dispersant having a carboxy group (COOH-containing polymer)
("DISPERBYK 190" manufactured by BYK-Chemie Japan K.K., acid value:
10 mgKOH/g, active ingredient: 40%, prime solvent: water), followed
by vigorous stirring. Thereto was gradually added 100 g of
2-dimethylaminoethanol (manufactured by Wako Pure Chemical
Industries, Ltd.). After stirring at 75.degree. C. for 1.5 hours, a
spherical silver powder was produced as a black precipitate.
Removal of a supernatant by means of decantation and a dilution
operation with water were repeated, and after dilution was
performed to an extent of 1,000 times the initial value, the
precipitate was recovered by means of suction filtration, thereby
obtaining a wet cake of silver nanoparticles protected by a carboxy
group-containing protective colloid (silver colloid particles).
(Preparation of Conductive Adhesive)
To the above-described wet cake was added 1,5-pentanediol
(manufactured by Wako Pure Chemical Industries, Ltd., boiling
point: 242.degree. C.) as a solvent, and thereafter, water was
removed while kneading in a mortar, thereby obtaining a silver
nanoparticle dispersion paste having a silver concentration of
88.0%.
To 100 parts of the above-described silver nanoparticle dispersion
paste were added 22.2 parts of 1,5-pentanediol and 8.8 parts of a
viscosity modifier ("BYK-431" manufactured by BYK-Chemie Japan
K.K., urea-modified polyamide, active ingredient: 25%, prime
solvent: isobutanol/monophenyl glycol), followed by kneading in a
mortar while applying a warm-air dryer, and the isobutanol and
monophenyl glycol contained in the viscosity modifier were removed,
thereby obtaining a conductive adhesive having a silver
concentration of 70.8%.
(Evaluation of Screen Printing Properties)
The above-described conductive adhesive was printed on a copper
substrate plated with nickel/gold (the adherend surface was gold)
by using a screen printing plate having a wire diameter of 18
.mu.m, 500 meshes, and an emulsion thickness of 10 .mu.m, thereby
forming a comb pattern of L/S=50/50 .mu.m, which was then evaluated
according to the following criteria.
A: The wire width after printing is a wire width of less than
.+-.10% relative to the target wire width.
B: The wire width after printing is a wire width that does not
satisfy the above-described criteria.
(Adhesiveness and Dryness)
The above-described conductive adhesive was printed on a copper
substrate plated with nickel/gold (the adhesive surface was gold)
by using a screen printing plate having a wire diameter of 18
.mu.m, 500 meshes, and an emulsion thickness of 10 .mu.m, thereby
forming a pattern of 500 .mu.m.quadrature. (500 .mu.m.times.500
.mu.m) on the substrate. After printing, the resultant was allowed
to stand at room temperature (25.degree. C.) for 0, 30, 60, 180, or
300 minutes, respectively, followed by confirming with an optical
microscope on whether or not the printed material was dried.
Specifically, the printed material was shaven by tweezers, and the
case where the dried material separated was evaluated as
"separation". Subsequently, a chip was mounted on the printed
conductive adhesive pattern, and shear strength was confirmed. The
shear strength was measured with "Universal Bond Tester Series
4000" manufactured by DAGE under conditions of a test speed of 330
.mu.m/s and a test height of 50 .mu.m. In addition, with respect to
a sample which was obtained by immediately after printing, mounting
a chip and curing at 200.degree. C. for 90 minutes, in addition to
the shear strength, a failure mode was observed and evaluated on
whether it was cohesive failure (metallic bonding) or interfacial
separation (nonmetallic bonding). It is to be noted that as the
chip, a chip obtained by providing a film by sputtering with
titanium, platinum and gold in this order (the adhesive surface was
gold) on aluminum nitride was used.
(Specific Resistivity)
The above-described conductive adhesive was coated on a slide glass
(a trade name: "SLIDE GLASS S1225" manufactured by Matsunami Glass
Ind., Ltd.) with an applicator and baked at 200.degree. C. for 90
minutes to form a conductive film having a thickness of 3 .mu.m. A
specific resistivity of the conductive film was calculated from a
surface resistance obtained by a four-point probe method and a film
thickness obtained by a contact-type thickness meter.
Example 2
To 100 parts of the silver nanoparticle dispersion paste prepared
in Example 1 were added 16.7 parts of 1,5-pentanediol and 4.4 parts
of a viscosity modifier (BYK-431), followed by kneading in a mortar
while applying a warm-air dryer, and the isobutanol and monophenyl
glycol contained in the viscosity modifier were removed, thereby
obtaining a conductive adhesive having a silver concentration of
75%. The resulting conductive adhesive was evaluated in the same
manners as in Example 1.
Example 3
To 100 parts of the silver nanoparticle dispersion paste prepared
in Example 1 were added 9.7 parts of 1,5-pentanediol and 2.2 parts
of a viscosity modifier (BYK-431), followed by kneading in a mortar
while applying a warm-air dryer, and the isobutanol and monophenyl
glycol contained in the viscosity modifier were removed, thereby
obtaining a conductive adhesive having a silver concentration of
80%. The resulting conductive adhesive was evaluated in the same
manners as in Example 1.
Example 4
To 100 parts of the silver nanoparticle dispersion paste prepared
in Example 1 were added 9.8 parts of 1,5-pentanediol and 1.1 parts
of a viscosity modifier (BYK-431), followed by kneading in a mortar
while applying a warm-air dryer, and the isobutanol and monophenyl
glycol contained in the viscosity modifier were removed, thereby
obtaining a conductive adhesive having a silver concentration of
85%. The resulting conductive adhesive was evaluated in the same
manners as in Example 1.
Example 5
To 100 parts of the silver nanoparticle dispersion paste prepared
in Example 1 were added 33.4 parts of 1,5-pentanediol and 13.2
parts of a viscosity modifier (BYK-431), followed by kneading in a
mortar while applying a warm-air dryer, and the isobutanol and
monophenyl glycol contained in the viscosity modifier were removed,
thereby obtaining a conductive adhesive having a silver
concentration of 65%. The resulting conductive adhesive was
evaluated in the same manners as in Example 1.
Comparative Example 1
The silver nanoparticle dispersion paste prepared in Example 1 was
used as it was and evaluated in the same manners as in Example
1.
Comparative Example 2
A paste obtained by adding 1,5-pentanediol to the silver
nanoparticle dispersion paste prepared in Example 1 to make the
silver concentration to 70% was used and evaluated in the same
manners as in Example 1.
Comparative Example 3
To 100 parts of a silver nanoparticle dispersion paste prepared in
the same manner as that in Example 1 except for changing the
solvent to butyl carbitol acetate were added 4.4 parts of butyl
carbitol acetate and 5.6 parts of a thickening agent ("EC-200"
manufactured by Nissin Kasei Co., Ltd., high-molecular weight ethyl
cellulose, active ingredient: 15%, prime solvent: butyl carbitol
acetate), followed by kneading in a mortar, thereby obtaining a
conductive adhesive having a silver concentration of 80%. The
resulting conductive adhesive was evaluated in the same manners as
in Example 1.
Comparative Example 4
To 100 parts of a silver nanoparticle dispersion paste prepared in
the same manner as that in Example 1 except for changing the
solvent to butyl carbitol acetate were added 4.4 parts of butyl
carbitol acetate and 21.3 parts of a thickening agent (EC-200),
followed by kneading in a mortar, thereby obtaining a conductive
adhesive having a silver concentration of 70%. The resulting
conductive adhesive was evaluated in the same manners as in Example
1.
Comparative Example 5
The same evaluations as in Example 1 were performed, except that
22.2 parts of 1,5-pentanediol and 5.5 parts of a polymer having a
carboxyl group (DISPERBYK 190) as a viscosity modifier were added
to 100 parts of the silver nanoparticle dispersion paste prepared
in Example 1, followed by kneading in a mortar while applying a
warm-air dryer, the water contained in the viscosity modifier was
removed, thereby obtaining a conductive adhesive having a silver
concentration of 70%.
The evaluation results of the adhesives obtained in the Examples
and Comparative Examples are shown in Table 1.
TABLE-US-00001 TABLE 1 Shear strength (kgf/chip) Viscosity Screen
Standing time until chip mounting after Specific Silver modifier/
printing printing/min Failure resistivity concentration Viscosity
silver 100 properties 0 30 60 180 300 mode (.mu..OMEGA. cm) (%)
modifier (parts) Ex. 1 A 0.84 0.79 0.81 0.83 0.75 Cohesive 4 71
Polyamide 2.5 failure Ex. 2 A 1.4 1.5 1.3 1.4 x Cohesive 3 75
Polyamide 1.3 failure Ex. 3 A 1.8 1.7 1.7 x x Cohesive 3 80
Polyamide 0.6 failure Ex. 4 A 2.4 1.8 1.9 x x Cohesive 3 85
Polyamide 0.3 failure Ex. 5 A 0.61 0.65 0.65 0.59 0.64 Cohesive 4
65 Polyamide 3.8 failure Comp. A 2.8 1.8 x x x Cohesive 3 88 No 0
Ex. 1 failure Comp. B 1.2 1.1 1.1 1.3 1.2 Cohesive 3 70 No 0 Ex. 2
failure Comp. A 0.04 0.03 0.03 x x Interfacial 3 80 Ethyl 1 Ex. 3
separation cellulose Comp. B 0.03 0.02 0.03 0.03 x Interfacial 3 70
Ethyl 3.6 Ex. 4 separation cellulose Comp. B 0.06 0.04 0.05 0.08 x
Interfacial 3 70 COOH- 2.5 Ex. 5 separation containing polymer
As is clear from the results of Table 1, the adhesives of the
Examples are excellent in screen printing properties and
adhesiveness, whereas the adhesives of the Comparative Examples are
poor in adhesiveness or screen printing properties.
While the invention has been described in detail and with reference
to specific embodiments thereof, it will be apparent to one skilled
in the art that various changes and modifications can be made
therein without departing from the spirit and scope of the present
invention.
The present application is based on Japanese Patent Application No.
2012-239957 filed on Oct. 31, 2012, the contents of which are
incorporated herein by reference.
INDUSTRIAL APPLICABILITY
The conductive adhesive of the present invention can be utilized as
an adhesive between inorganic materials such as metal materials,
etc., and for example, it can be utilized for formation of
electrodes or circuits of electronic components and the like,
adhesion between components, and the like.
* * * * *
References